1. Field of the Invention
The present invention relates to a method for welding a piston head member with a piston skirt member of a piston with a cooling duct by friction welding, wherein the hollow space of the cooling duct preferably contains no protruding welding beads.
2. Description of Related Art
The connection between two parts of a piston having a cooling duct by friction welding is known. International Patent Application WO 2006/034862 A1 teaches a piston having a cooling duct, where the piston head is connected with the piston skirt member by friction welding the walls of the cooling duct resulting in weld beads on both sides of the weld. The aforesaid weld beads in the cooling duct negatively influence the cooling medium.
From German Patent Application DE 10 2006 01 044 A1, it is known to form concomitantly two welds with small weld beads by friction welding, whereas the beads in the cooling duct must be machined from outside leaving a smooth surface within the cooling duct.
So until now, it was necessary to use mechanical machining to obtain a smooth surface in the cooling duct of a friction welded piston with a cooling duct so that the cooling oil has an undisturbed free flow pathway in the piston to enable optimum cooling thereof.